FIELD PROBLEMS IN DETERMINING THE 



MAXIMUM EXTENT OF PLEISTOCENE 



GLACIATION ALONG THE EASTERN CANADIAN 



SEABOARD— A GEOGRAPHER'S POINT OF VIEW* 



J. D. IVESf 

 Geographical Branch, Department of Mines and Technical Surveys, Ottawa, Canada 



The main obstacles to evaluation of the maximum extent of glaciation in 

 eastern Canada are simply a combination of vast area, difficulty of access 

 and acute shortage of field investigators. These problems naturally pervade 

 the entire discussion which follows and they cannot be overstressed : however, 

 some of the gaps can be partially filled by reference to work in other sectors 

 of the North Atlantic, particularly in Norway and Iceland. It should be 

 apparent, moreover, that even these much smaller areas have not been studied 

 in great detail and, as members of the symposium will undoubtedly agree, 

 the interpretation of the available field evidence has divided us into two camps 

 — the protagonists, and the antagonists of the nunatak hypothesis. 



It is apparent from the hterature that much controversy has arisen con- 

 cerning the significance of certain glacial erratic blocks on high coastal 

 summits. Bergstrom, Hoppe and others inaintain that blocks on the Lofoten 

 Island summits are glacial erratics (Bergstrom, 1959; Hoppe, 1959) and the 

 tendency is to proceed from this point to the suggestion that all the Lofoten 

 summits must therefore have been inundated at one and the same time, 

 namely, during the final glaciation. Dahl, on the other hand, has enunciated 

 a plea that evidence for the existence of true glacial erratics must include 

 positive proof that the rock in question is foreign geologically to the base- 

 ment upon which it rests — in other words, the possibiUty that the rock is an 

 erosion residual must be definitely excluded (Dahl, 1961). Also, absence of 

 proof of glaciation does not warrant the conclusion that glacier ice has not 

 passed across a specific area, nor does positive proof of glaciation determine 

 which particular glaciation was involved. One of the more difficult field 

 problems is to determine the relative age of an erratic. Usually this is impossible 

 and the deduction frequently resorted to is highly subjective. Neither is it 



*Published with the permission of the Director, Geographical Branch, Dept. Mines 

 and Technical Surveys, Ottawa. 



t Senior Geographer, Geographical Branch, Ottawa Canada. 



337 



